Armor piercing projectile, such as may be fired by tanks, artillery, machine guns etc. generally rely on a pointed tip of hardened steel, tungsten, etc. to penetrate a target. The pointed tip of the armor piercing projectile presents a small impact area and, therefore, a high impact stress. The high impact stress allows the armor piercing projectile to pierce and penetrate a structure.
Armor or ballistic resistant materials directed at defeating armor piercing projectiles are generally selected for hardness. Harder materials offer several advantages for defeating armor piercing projectiles. First, harder materials provide a greater resistance to penetration. Harder materials, also, will be able to blunt, or flatten out the pointed tip of an armor piercing projectile. Blunting the pointed tip of a projectile will increase the impacting surface area of the projectile which will decrease the impacting stress applied by the projectile. Additionally, in the case of a harder material, if the projectile does not strike an armored structure normal to the surface, there is a possibility that a hard surface may deflect the projectile. Because of the benefits of high hardness materials, often the most effective armor is armor grade ceramics, such as CAP3 alumina or hot-pressed silicon carbide, which have hardness levels which exceed that found in conventional metals.
Hardness alone is not the only important property for armor materials. Desirably, the armor material will also be tough enough so that it can provide multi-hit capability or protection. While ceramic armor materials are very hard and provide good armor piercing protection, due to the brittleness of the material, ceramics do not generally provide multi-hit capability. Typically, after an initial impact, the ceramic material will fracture or shatter. To mitigate this effect, ceramic armor is often applied in the form of small hexagonal tiles. While the armor tiles still fracture after being hit, the fracture may be contained to only those tiles at the point of impact. Therefore, the damage and attendant loss of protection is limited only to those tiles struck by the projectile. The remainder of the armor system may remain generally intact, and the potential for penetration may be minimizes, since nearby panels will not be affected and overall protection is maintained as long as additional projectiles do not hit the same area.
While armoring steel often will not offer the same level of initial-hit protection provided by ceramics, for many applications armoring steel is used because it provides greater multi-hit protection. Unfortunately, for many applications involving aircraft or mobile ground systems including tanks and armored personal vehicles, a weight is a critical consideration. It is often desirable, or even necessary that the armor have relatively low density in order to minimize weight to allow for system transportability, system payload, and for range/fuel consumption. Ceramics have an inherent advantage in density compared to metals since they are made up of high fractions of relatively light elements such as oxygen (i.e. oxides) or carbon (i.e. carbides).
It is apparent, therefore, that no one material has all of the desired characteristics for armor piercing protection. Existing armoring steel exhibits advantageous multi-hit capability, but is heavy because of steel's relatively high density and the thicknesses of steel armor systems required to defeat incoming projectiles. By contrast, ceramic armor is lightweight and very hard, but does not offer multi-hit capability. Other lightweight metallic materials, such as aluminum, may have the toughness required to provide multi-hit capability, but these materials are generally soft and offer only limited ballistic resistance.
It is therefore an object of the present invention to provide a layered metallic material wherein the layers are selectively altered in their mechanical property characteristics to provide an overall layered configuration that optimizes the response of the layered material to a high impact focused stress, such as that provided by armor piercing projectiles.
In addition, it is an object of the present invention to provide the aforementioned layered metallic material, by the use of a layer of an iron based glass alloy material, and a layer of aluminum.
It is also an object of this invention to therefore provide an armor system which not only exhibits synergistic hardness and ductility characteristics, but which also provides multi-hit protection and is relatively lightweight.